INORGANIC RESPONSE 121 
more and more incomplete. These considerations may 
be found to afford an insight into the progressive diminu- 
tion of response in fatigued substances. 
Fatigue under continuous stimulation.—Fatigue is 
perhaps best shown under continuous stimulation. For 
example, in muscles, when fresh and not fatigued, the 
top of the tetanic curve is horizontal, or may even be 
ascending, but with long-continued stimulation the 
curve declines. The rapidity 
of this decline depends on the 
nature of the muscle and its 
previous condition. 
In metals I have found (a) (b) 
exactly parallel instances. In 8 
tin, so little lable to fatigue, (a The top of response-curve un- 
: der continuous stimulation in 
the top of the curve is hori- tin is horizontal or ascending 
7 A as in figure. (b) In platinum 
zontal or ascending ; or it may there is tapid decline owing to 
= 5 atigue. 
exhibit a slight decline. But 
the record with platinum shows the rapid decline due 
to fatigue (fig. 73). 
Taking any of these instances, say that in which 
fatigue is most prominent, it is found that short period 
of rest restores the original intensity of response. This 
affords additional proof of the fact that fatigue is due to 
overstrain, and that this strain, with its sign of attendant 
fatigue, disappears with time. 
Staircase effect.—We shall now discuss an effect 
which appears to be the direct opposite of fatigue. 
This is the curious phenomenon known to physiologists 
as ‘the staircase’ effect, in which successive uniform 
stimuli produce a series of increasing responses. This 
